An electronic system may include one or more integrated circuit devices, such as a microprocessor, an input/output (I/O) unit, a programmable gate array, and a memory device. The memory device may include a redundancy repair circuit. Functions or circuit configurations of devices having the redundancy repair circuit may be changed when a predetermined programming operation is performed thereon after the devices are fabricated.
Memory devices may be classified into volatile memory devices and nonvolatile memory devices. A phase change memory device is one well known nonvolatile memory device. The phase change memory device may include an array of phase change memory cells disposed in a cell region of a substrate. The phase change memory cell includes a switching device and a data storage element serially connected to the switching device. The data storage element may have top and bottom electrodes and a phase change material layer therebetween, whereon one of the electrodes is electrically connected to the switching device. The phase change material may comprise a chalcogenide material.
However, when one of the cells is defective, the phase change memory device may fail to properly operate. To cope with this, a technique of providing the redundancy repair circuit is widely employed. The redundancy repair circuit includes one or more fuses in a fuse region of the substrate. A test process is used to find the defective cell, and a repair process is used to cut the fuse connected to the defective cell. In this case, the defective cell is replaced with a corresponding redundancy memory cell by the redundancy repair circuit.
The method of cutting the fuse may include melting the fuse with a laser beam. In this case, in order to prevent an adjacent fuse from being damaged while the fuse connected to the defective cell is cut, an interval between the fuses should be larger than the region irradiated with the laser beam. Thus, reduction of the interval between fuses may be limited by the size of the region irradiated by the laser beam. In addition, it may be difficult to stack other devices on the fuses. Consequently, employing the method of cutting fuses with a laser beam may reduce the integration density of the device.
In order to deal with this problem, the fuse connected to the defective cell may be electrically cut. Conventional fuses are formed of a polysilicon layer or a metal layer. A high driving current may be supplied to cut the fuse connected to the defective cell. As a high driving current may be needed, the size of the switching device may also need to be relatively large. The large switching device may consume excessive area and/or power.
Meanwhile, other methods of forming a fuse are disclosed in Korean Patent Publication No. 2003-0045603 entitled “Programmable Element, Programmable Circuit and Semiconductor Device” to Toyoshima Yoshiaki, corresponding to U.S. Pat. No. 6,703,680, issued Mar. 9, 2004. Yet other methods of forming a fuse are disclosed in Korean Patent Publication No. 10-2005-0003326 entitled “Three Dimensional IC Structure and Fabricating Method Thereof for Forming Various Semiconductor Devices Having Vertical Structure By Applying Three-Dimensional IC” to Sang Yun Lee, corresponding to U.S. Pat. No. 7,052,941, issued May 30, 2006.
Finally, a fuse device is described in Japanese Patent Publication No. 2004-103604 entitled “Fuse Device” to Matsuo Mie et al. As described in the English language translation of the Abstract of this patent publication, the fuse device is equipped with an insulating film formed on a semiconductor substrate, and a fuse which is formed inside the insulating film and changed in resistance with the phase transition caused by the heat from a heating means to set information. The phase transition fuse is made of a chalcogen or an alloy bringing about a martensite transformation. After the fuse is heated, it is quickly cooled down so as to store the information.